1. Field of the Invention
The present invention relates to an electrolyte for a fuel cell that has improved proton conductivity, heat resistance, and mechanical strength, and a fuel cell employing the same.
2. Description of the Background
Due to the reduction in available global energy resources, the development and use of clean energy is required all over the world. For example, the development of transportation networks and the increase in the number of vehicles have brought about serious air pollution problems due to exhaust gases of internal combustion engines of automobiles. Electric automobiles are being developed to solve these problems. For example, a lightweight fuel cell that can be handled easily and does not contaminate the air may be used as an energy source for automobiles. The fuel cell may also be used as an energy source in home settings.
Fuel cells can be classified into categories including alkaline fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid polymer electrolyte fuel cells, solid polymer fuel cells, and the like, depending on the type of electrolyte used. The solid polymer electrolyte fuel cell, which is operable at low temperatures, can be handled easily, and has high output power, is emerging as a leading energy source for electric automobiles, homes, and the like.
A proton conducting membrane that is used for solid polymer electrolyte fuel cells should have high ionic conductivity for protons that are involved in an electrode reaction of a fuel cell. For example, a fluorine-based polymer containing a superacid group has been used as a proton conducting membrane, but is very expensive. In addition, since a possible proton conducting medium is water, water should be supplied by continuous humidification.
Japanese Patent Publication No. 2002-280019 and No. 2002-358978 disclose a proton conducting membrane comprising an ion dissociating group such as a carboxylic acid group, a sulfonic acid group, and a phosphate group in an aromatic skeleton. However, such an ion dissociating group may easily separate at high temperatures, and the proton conducting membrane may have poor flexibility and proton conductivity. In addition, Japanese Patent Laid-Open Publication No. Hei 8-504293 includes a similar description, but does not disclose proton conductivity.
Furthermore, a method exists for introducing an active hydrogen group by reacting polybenzimidazole with sultone. However, this method can introduce only a sulfonic acid group and may not be applied to other active hydrogen groups.